Trim the chicken and cut larger breasts into tender-sized pieces. Place a piece of plastic wrap over the tenders and flatten them to the same thickness using a meat tenderizer. Alternately, you can butterfly the breasts into thinner pieces. This will allow them to cook more evenly. Place the chicken breasts in a large Ziploc bag or shallow container.
Whisk together the Dijon mustard, honey, garlic, lemon juice, paprika, salt, pepper, and cayenne pepper in a small bowl. Reserve half of the sauce for serving. Pour the remaining half the sauce over the chicken and marinate in the refrigerator for a minimum of 30 minutes (up to overnight). We prefer to marinate ours for 2-4 hours.
Drizzle ½ tablespoon of avocado oil in a large skillet and warm over medium-high heat. Once the oil is hot, add the chicken in a single layer in the pan. Discard leftover marinade. Brown on one side for 4 to 5 minutes. Flip the chicken over and brown for another 4 to 5 minutes. Cook time will depend on the thickness of your chicken and the type of pan used, so for the best results use a meat thermometer.
Once the internal temperature reaches 160℉, drizzle the reserved honey mustard over the chicken. Warm for another minute, then remove from heat and serve. Note: the final internal temperature of the chicken should be 165℉ when done.